The impact of fibrinolytic therapy for ST-segment-elevation acute myocardial infarction.

As privileged witnesses of the initiation and widespread use of reperfusion therapy the authors review the history of fibrinolytic therapy and of tissue-plasminogen activator (t-PA) more particularly and the current indications for its use in the era of mechanical reperfusion.

Effects of insulin sensitizers on plaque vulnerability associated with elevated lipid content in atheroma in ApoE-knockout mice.

Acute coronary syndromes are generally precipitated by rupture of lipid-laden, relatively acellular, vulnerable atherosclerotic plaques with thin fibrous caps. We investigated whether a high-fat diet alters insulin sensitivity and whether insulin sensitizers (troglitazone and rosiglitazone) alter the composition of otherwise lipidladen atherosclerotic plaques in mice deficient in apolipoprotein E (ApoE). ApoE-knockout mice were fed a high-fat (n=30) or standard chow (n=10) diet for two weeks. Thereafter, those fed the high-fat diet were treated with troglitazone (n=10), rosiglitazone (n=10) or no drug (n=10) for 16 weeks beginning at 8 weeks of age. Carbohydrate metabolism was assessed with intraperitoneal glucose tolerance tests and insulin tolerance tests. Plaque composition was characterised with confocal laser scanning microscopy. The high-fat diet induced insulin resistance in the absence of weight gain. Compared with control animals on the high-fat diet, animals given troglitazone (400 mg/kg/day) or rosiglitazone (4 mg/kg/day) had significantly less area under the curve (AUC) for insulin ( p<0.05) and glucose disposal ( p<0.05). Despite significant increases in insulin sensitivity with drug treatment, no change in HDL-cholesterol and triglyceride levels, nor reduction in atheroma size or lipid content was noted. Thus, improvement in insulin resistance induced by a high-fat diet in this animal model of vasculopathy did not alter plaque composition.

Augmentation of inhibitory effects of glycoprotein IIb-IIIa antagonists in patients with diabetes.

BACKGROUND: Patients with diabetes mellitus and acute coronary syndromes (ACS) derive enhanced benefit from treatment with glycoprotein (GP) IIb-IIIa inhibitors. To determine mechanisms potentially responsible we characterized the binding of fibrinogen to platelets from patients with and without diabetes in the presence and absence of GP IIb-IIIa antagonists. METHODS: GP IIb-IIIa antagonists (tirofiban, eptifibatide, and abciximab) were added in vitro to blood from patients with and without diabetes. Binding of fibrinogen to activated GP IIb-IIIa was assessed with the use of flow cytometry. The kinetics of binding of I(125)-abciximab and I(125)-fibrinogen to washed platelets from subjects with and without diabetes mellitus were determined. Glycation of platelet membrane proteins was measured with the fructosamine assay. RESULTS: In the presence of GP IIb-IIIa antagonists, activation-induced binding of fibrinogen to platelets was reduced to a greater extent (p<0.02) in blood from patients with diabetes. The greater inhibition in blood from patients with diabetes was seen with pharmacologic concentrations of tirofiban (50 ng/ml, by 27%), eptifibatide (1.5 microg/ml, by 24%), and abciximab (2 mg/ml, by 12%). Whereas the binding of I(125)-abciximab was similar to platelets from patients with diabetes and those without, the rate of binding of I(125)-fibrinogen was decreased with platelets from patients with diabetes. Binding after 5 min was reduced by 46% in those with diabetes (p<0.05). Platelet membrane proteins from patients with diabetes were glycated to a greater extent compared with those without diabetes. CONCLUSION: GP IIb-IIIa antagonists inhibit platelet activation to a greater extent in blood from patients with diabetes. The decreased rate of binding of fibrinogen early after activation of platelets appears to be a consequence of glycation and may promote inhibition by GP IIb-IIIa antagonists.

Effect of fatty acid chain length and thioesterification on the augmentation of expression of plasminogen activator inhibitor-1.

BACKGROUND AND AIM: Concentrations in blood of plasminogen activator inhibitor type 1 (PAI-1) and circulating free (non-esterified) fatty acids (FFA) are increased in diabetes and may accelerate atherosclerosis. We have shown that FFA increase expression of PAI-1 by activation of a transcription factor that binds to the repeated sequence 5'-TG(G/C) 1-2CTG-3'. This study was designed to determine whether FFA chain length, saturation, or both affect agonist properties and whether agonist properties are mediated by activated, thioesterified FFA (fatty acyl-CoA). METHODS AND RESULTS: Human hepatoma cells were exposed to selected FFA associated with bovine serum albumin (BSA). Triacsin C (5 microM) was used to inhibit production of fatty acyl-CoA. PAI-1 was assayed by enzyme linked immunosorbent assay. Maximal induction of PAI-1 was similar with medium and long chain FFA (fold induction of PAI-1 accumulated in conditioned media compared with control: C10 = 1.8 +/- 0.1, C12 = 2.0 +/- 0.1, C14 = 2.0 +/- 0.2, C16 = 1.4 +/- 0.1, C18 = 1.6 +/- 0.1, C20 = 1.32 +/- 0.1, p < 0.005 for each compared with control). Increased unsaturation did not alter the agonist properties of FFA (fold induction with C16: 0 = 1.4 +/- 0.1, C16: 1 = 1.4 +/- 0.1; C18: 0 = 1.6 +/- 0.1, C18: 1 = 1.5 +/- 0.1, C18: 2 = 1.6 +/- 0.1, C18: 3 = 1.4 +/- 0.1 and C20: 4 = 1.3 +/- 0.1, C20: 5 = 1.4 +/- 0.1, n = 6). However, maximal effects were seen with lower concentrations of longer chain FFA. Triacsin C consistently attenuated effects of FFA. CONCLUSIONS: Longer chain FFA exhibit maximal effects at lower concentrations. Augmented expression of PAI-1 is mediated by the fatty acyl-CoA derivative. These criteria identify targets for therapy designed to normalize expression of PAI-1 and retard progression of atherosclerosis in subjects with elevated concentrations of FFA in blood including those with insulin resistance.

Double-blind, randomized trial of an anti-CD18 antibody in conjunction with recombinant tissue plasminogen activator for acute myocardial infarction: limitation of myocardial infarction following thrombolysis in acute myocardial infarction (LIMIT AMI) study.

BACKGROUND: Inhibition of leukocyte adhesion can reduce myocardial infarct size in animals. This study was designed to define the safety and efficacy of a recombinant, humanized, monoclonal antibody to the CD18 subunit of the beta2 integrin adhesion receptors (rhuMAb CD18), in reducing infarct size in patients treated with a thrombolytic agent. METHODS AND RESULTS: The Limitation of Myocardial Infarction following Thrombolysis in Acute Myocardial Infarction Study (LIMIT AMI) was a randomized, double-blind, placebo-controlled, multicenter study conducted in 60 centers in the United States and Canada. A total of 394 subjects who presented within 12 hours of symptom onset with ECG findings (ST-segment elevation) consistent with AMI were treated with recombinant tissue plasminogen activator and were also given an intravenous bolus of 0.5 or 2.0 mg/kg rhuMAb CD18 or placebo. Coronary angiography was performed at 90 minutes, 12-lead ECGs were obtained at baseline, 90, and 180 minutes, and resting sestamibi scans were performed at >/=120 hours. Adjunctive angioplasty and use of glycoprotein IIb/IIIa antiplatelet agents at the time of angiography were discretionary. There were no treatment effects on coronary blood flow, infarct size, or the rate of ECG ST-segment elevation resolution, despite the expected induction of peripheral leukocytosis. A slight trend toward an increase in bacterial infections was observed with rhuMAb CD18 (P=0.33). CONCLUSIONS: RhuMAb CD18 was well tolerated but not effective in modifying cardiac end points.

Platelet reactivity in coronary ostial blood: a reflection of the thrombotic state accompanying plaque rupture and of the adequacy of anti-thrombotic therapy.

BACKGROUND: Optimal anti-thrombotic therapy for acute coronary syndromes (ACS) should suppress pro-thrombotic activity at the site of plaque rupture. We sought to determine whether platelet reactivity is increased in blood in the immediate vicinity of a ruptured plaque and is apparent even when blood is obtained by sampling from a catheter placed proximal to the lesion. METHODS: Blood was obtained from a catheter placed in the aorta and from the same catheter after engaging the culprit coronary artery. Platelet reactivity was determined with the use of flow cytometry by surface expression of P-selectin. RESULTS: In preliminary studies we demonstrated that a marker of thrombin activity, fibrinopeptide A, was similarly increased in blood taken from the coronary sinus and coronary arterial ostium of patients with ACS. Subsequently blood was obtained from the aorta and coronary arterial ostium through a coronary guide catheter for assessment of platelet reactivity in 23 subjects with ACS and 22 subjects with stable angina. The percentage of platelets expressing P-selectin in response to 0.2 microM adenosine diphosphate (ADP) was greater in coronary arterial samples from patients with ACS (aorta=6.1+/-1%, coronary artery=8.8+/-1.6%, p=0.02) compared with that in patients with stable symptoms (aorta=6.9+/-1.2, coronary artery=6.5+/-1.4, p=NS). CONCLUSIONS: Coronary arterial blood obtained from the ostium through a coronary guide catheter can be used to determine whether thrombin activity and platelet reactivity are increased in the immediate vicinity of a ruptured atherosclerotic plaque. The simplicity of the approach developed should facilitate its use in future studies designed to determine the impact of optimal suppression of platelet reactivity and the pro-thrombotic state before coronary interventions on short- and long-term clinical outcomes.

Stimulation in vivo of expression of intra-abdominal adipose tissue plasminogen activator inhibitor Type I by proinsulin.

AIMS/HYPOTHESIS: Impaired fibrinolytic system capacity secondary to increased plasminogen activator inhibitor type-1 expression has been suggested as a pathogenetic link between insulin resistance and increased cardiovascular risk in patients with Type II (non-insulin-dependent) diabetes mellitus, obesity, or both. In patients with syndromes of insulin resistance including those with Type II diabetes, precursors of insulin such as proinsulin can constitute more than 50% of insulin-like molecules in blood. The aim of this study was to determine whether proinsulin can increase plasminogen activator inhibitor type-1 expression in intra-abdominal adipose tissue in vivo, potentially contributing to the increased PAI-1 seen with insulin resistance. METHODS: Lightly sedated normal rabbits were given intravenous proinsulin, insulin, or vehicle alone under euglycaemic clamp conditions with serial sampling of blood and assessment of PAI-1 expression in visceral fat. RESULTS: Both proinsulin and insulin increased expression of plasminogen activator inhibitor type-1 in intra-abdominal adipose tissue, 5.3-fold (p = 0.006 vs control) and 2.5-fold (p = 0.031 vs control) respectively. PAI-1 inhibitor activity in blood peaked 3 h after administration of each, 5.1-fold, p = 0.020, and 3.4-fold, p = 0.004, respectively but did not change under control conditions. CONCLUSION/INTERPRETATION: Hyperproinsulinaemia can contribute to increased expression of plasminogen activator inhibitor type-1 in intra-abdominal adipose tissue implicated in increasing PAI-1 activity in blood, impaired fibrinolysis, and accelerated atherogenesis typical of Type II diabetes.

Platelet reactivity characterized prospectively: a determinant of outcome 90 days after percutaneous coronary intervention.

BACKGROUND: Platelet activation is pivotal in the pathogenesis of complications after percutaneous coronary interventions (PCI). We previously reported substantial interindividual variability in activation of glycoprotein (GP) IIb/IIIa in response to a low concentration of ADP. We assessed GP IIb/IIIa activation prospectively to determine whether this could differentiate patients at low risk from those at high risk for complications early and late after PCI. Methods and Results-- A total of 112 patients undergoing PCI were studied. Platelet reactivity was determined with the use of flow cytometry. Patients were classified into high and low platelet reactivity groups on the basis of extent of activation of GP IIb/IIIa in response to 0.2 micromol/L ADP. The median value was used for differentiation. The incidence during 90-day follow-up interval of a composite end point (myocardial infarction, urgent revascularization, or repeat revascularization) was determined in each group. Follow up was completed in all 112 patients. The 2 groups were similar with respect to diverse clinical characteristics. Nevertheless, the incidence of the composite end point occurred in 26.8% of the high and 7.1% in the low platelet reactivity group (P=0.01). The difference in the composite end point was most striking during the 30- to 90-day interval after PCI (16.7% versus 1.9%; P=0.02). Repeat revascularization was more frequent in those with increased platelet reactivity (17.9% versus with 3.6%, P=0.029). CONCLUSIONS: Prospective assessment of platelet GP IIb/IIIa activation permits stratification of patients into low- and high-risk groups with respect to adverse events after PCI.

Angiotensin-converting enzyme inhibition attenuates hypofibrinolysis and reduces cardiac perivascular fibrosis in genetically obese diabetic mice.

BACKGROUND: Obesity and insulin resistance are associated with accelerated macrovascular and microvascular coronary disease, cardiomyopathic phenomena, and increased concentrations and activity in blood of plasminogen activator inhibitor type 1 (PAI-1), the primary physiological inhibitor of fibrinolysis. METHODS AND RESULTS: To determine whether hypofibrinolysis in blood and tissues and its potential sequelae could be attenuated pharmacologically, we studied genetically modified obese mice. By 10 weeks of age, obese mice exhibited increases in left ventricular weight and glucose and immunoreactive insulin in blood. PAI-1 activity in blood measured spectrophotometrically was significantly elevated as well. The difference compared with values in lean controls widened by 20 weeks of age. Perivascular fibrosis in coronary arterioles and small coronary arteries was evident in obese mice 10 and 20 weeks of age, paralleling increases in PAI-1 and tissue factor expression evident by immunohistochemical image analysis, in situ hybridization, and reverse transcription-polymerase chain reaction. Inhibition of ACE activity initiated in obese mice 10 weeks of age and continued for 20 weeks arrested the increase in PAI-1 activity in blood and in cardiac PAI-1 and tissue factor mRNA as well as coronary perivascular fibrosis. CONCLUSIONS: Thus, inhibition of proteo(fibrino)lysis and augmented tissue factor expression in the heart precede and may contribute to the coronary perivascular fibrosis seen with obesity and insulin resistance. Furthermore, inhibition of ACE activity can attenuate all 3 phenomena.

Fibrin specificity of plasminogen activators, rebound generation of thrombin, and their therapeutic implications.

Optimal induction of coronary thrombolysis depends in part upon the nature of the specific plasminogen activator used. The two general classes of plasminogen activators available clinically differ in a fundamental respect delineated by the term, clot selectivity. Clot selective agents are less prone to induce plasminemia and consequent occult activation of the coagulation cascade than are non-selective agents. However, under clinical conditions, all plasminogen activators result in some activation of the cascade with consequent generation of thrombin. Accordingly, optimal therapy requires the use of conjunctive anticoagulation to preclude the deleterious effects of rebound generation of thrombin, which has been well documented biochemically. The potential value of antiplatelet agents that can attenuate the positive feedback loop between activation of platelets and markedly amplified generation of thrombin in the setting of coronary thrombolysis is under active exploration. With appropriate monitoring of the efficacy of such agents in vivo it should be possible to enhance even further the benefits that can be conferred by pharmacologically induced coronary thrombolysis.

High glucose concentrations induce oxidative damage to mitochondrial DNA in explanted vascular smooth muscle cells.

Oxidative stress is considered to be one of the mechanisms leading to atherosclerosis. It occurs in response to injury or to altered metabolic state. Alterations in cell growth (proliferation or apoptosis) can also contribute to the pathogenesis of atherosclerosis and is influenced by oxidative stress. Smooth muscle cells (SMC) from aortic explants of JCR:LA-cp homozygous cp/cp corpulent rats who are genetically predisposed to develop atherosclerosis exhibit increased SMC proliferation, which can be attenuated by exercise and food restriction. This study was conducted to characterize the effects fo oxidative stress and high glucose media on cell growth and its relationship to mitochondrial DNA integrity and gene expression in explanted aortic SMC from corpulent and lean JCR:LA-cp rats. The results show that SMC from the cp/cp rat appear to be resistant to oxidant-induced cell death and that they accumulate mitochondrial DNA mutations, probably as a result of a reduction in apoptosis. These data suggest that susceptibility to age- and glucose-related atherosclerosis may be related to alterations in redox signaling.

Quantification by flow cytometry of the efficacy of and interindividual variation of platelet inhibition induced by treatment with tirofiban and abciximab.

BACKGROUND: After exposure of platelets to abciximab and tirofiban in vitro, we have observed variable inhibition of fibrinogen binding and a lack of inhibition of alpha-granule degranulation. DESIGN: To determine whether such changes occur with treatment, platelet reactivity was assayed in blood from 50 patients receiving abciximab or tirofiban. METHODS: Platelet reactivity was determined before and during steady-state infusions of abciximab (0.125 microg/kg/min) or tirofiban, with either the PRISM-PLUS dosage (0.1 microg/kg/min) or the RESTORE dosage (0.15 microg/kg/min). Fibrinogen binding and P-selectin expression were determined by flow cytometry after stimulation of platelets with ADP (0.2 or 1 microM) or thrombin-receptor agonist peptide (TRAP, 25 microM). RESULTS: Both dosages of tirofiban and abciximab reduced fibrinogen binding in response to 0.2 microM ADP comparably. However, fibrinogen binding in response to 1.0 microM ADP or 25 microM TRAP was inhibited to a greater extent by the RESTORE dosage of tirofiban and abciximab than by the PRISM-PLUS dosage of tirofiban (P< 0.05). Furthermore, only the RESTORE dosage of tirofiban and abciximab reduced P-selectin expression in response to ADP. Inhibition with each regimen varied markedly between patients. CONCLUSIONS: The RESTORE dosages of tirofiban and abciximab each inhibit fibrinogen binding and alpha-granule degranulation similarly. However, substantial interindividual variation in inhibition of fibrinogen binding is evident.

Bingo vs. physical intervention in stimulating short-term cognition in Alzheimer's disease patients.

Past research has shown that pharmacological measures can enhance cognitive and functional capacities for patients with Alzheimer's disease, but may result in unacceptable side effects. Investigations using nonpharmacological treatments are limited. This study evaluates the therapeutic effect of the game of Bingo as cognitive stimulation, versus daily physical activity, on short-term memory, concentration, word retrieval, and word recognition. Informed consent was obtained from the designated representatives of 50 subjects from six community adult day care centers on Long Island. The results show that cognitive stimulation enhanced performance on the Boston Naming Test and a Word List Recognition Task; physical intervention, however, did not reach statistical significance. Thus, a simple cognitive activity such as Bingo can be of great value to the daily management of Alzheimer's patients.

Time and dose dependent augmentation of inhibitory effects of abciximab by aspirin.

Aspirin and abciximab independently decrease the incidence of cardiac events. To identify potential interactions, antiplatelet effects of abciximab were characterized in blood from healthy subjects given aspirin. Platelet activation was determined in whole blood with and without abciximab (2 microg/ml) added in vitro. Flow cytometry was used to quantify fibrinogen binding (glycoprotein IIb-IIIa activation). Binding of fluorochrome-labeled and 125I-labeled abciximab was determined before and after exposure to aspirin. In blood from subjects given aspirin for 5 days, abciximab-induced inhibition of the capacity to bind fibrinogen in response to 1 microM ADP was greater when the daily dose had been 325 mg compared with 81 mg (% inhibition: no aspirin 53 +/- 6; 81 mg daily 62 +/- 5; 325 mg daily 69 +/- 6). The effect of 5 daily doses of aspirin was greater than that of one. Larger single doses elicited larger effects (% inhibition 2 h after 325 mg 59 +/- 6; 2 h after 650 mg 78 +/- 5). Neither salicylsalicylic acid nor naproxen sodium potentiated the effect of abciximab. Exposure of platelets to 14C-acetylsalicylic acid led to acetylation of glycoprotein IIb and IIIa. Binding of 125I-abciximab to platelets was increased after 30 and 60 min. Acetylation of glycoprotein IIb-IIIa by aspirin augments inhibitory effects of abciximab in a dose- and time-dependent manner by increasing binding of abciximab to platelets.

Attenuation by fibrates of plasminogen activator inhibitor type-1 expression in human arterial smooth muscle cells.

Human atherosclerotic lesions exhibit increased expression of plasminogen activator inhibitor type-1 (PAI-1) that has been implicated in atherogenesis. Although vascular smooth muscle cells are a predominant source of PAI-1 expression potentially favorable modulation of PAI-1 expression by fibrates has not yet been characterized in these cells. Human aortic smooth muscle cells were exposed to selected growth factors. PAI-1 expression was stimulated most powerfully by TGF-beta (EC50 = 0.2 ng/ml, up to 12-fold increase). Gemfibrozil inhibited basal PAI-1 expression by 23% (p = ns) and TGF-beta-induced PAI-1 expression by 52% (p = 0.017) whereas t-PA and total protein synthesis was not affected. Changes in PAI-1 protein accumulation reflected PAI-1 gene expression attributable to modulation of half-life of PAI-1 mRNA by gemfibrozil. Inhibition by other fibrates was less. Gemfibrozil specifically attenuates TGF-beta-induced PAI-1 expression in human arterial smooth muscle cells. Thus, fibrates are promising agents for normalizing increased PAI-1 expression in arterial walls in patients in whom PAI-1 expression is increased.